1. Technical Field
The present disclosure relates to a heat treating furnace, and more particularly to a heat-treating furnace, such as a firing furnace, a degreasing furnace, or the like, for heat-treating a material to be heat-treated, including a step of firing a green ceramic body and a step of removing a binder before the firing step, for example, in the manufacture of ceramic electronic components.
2. Background Art
FIG. 6 is a drawing showing an example of a conventional heat-treating furnace. In general, a firing furnace including a so-called module heater 64 which includes a heater 63 disposed in a heat insulator 62, such as a ceramic wool material, around a heat-treatment region 65 in a case 61 as schematically shown in FIG. 6 is widely used as a firing furnace for firing a material to be fired, such as a ceramic molding (green ceramic body) in a process for manufacturing a ceramic electronic component.
However, such a firing furnace is mainly used for firing a ceramic molding after the binder removing step and is generally difficult to use for binder removal.
This is because when a binder is removed using a heat-treating furnace provided with the module heater 64 as shown in FIG. 6 in which a material 66 to be fired, such as a ceramic molding (green ceramic body), is placed in the heat treatment region 65, a vapor of the binder permeates into the heat insulator 62 of the module heater 64 which is composed of ceramic wool. The vapor condenses and solidifies in the heat insulator 62, thereby causing a large difference in thermal expansion coefficient between a portion in which the binder vapor has permeated and a portion in which the binder vapor has not permeated, thus causing peeling or breakage of the heat insulator 62 in some cases.
Therefore, when binder removal and subsequent firing are continuously performed, a heat treating furnace provided with an inner case (inner muffle) is used in order to prevent binder vapor produced in the binder removing step from permeating into the heat insulator composed of a ceramic wool material.
That is, the inner case is provided inside the case in order to prevent the binder vapor produced in the binder removing step from condensing and adhering to the heat insulator by cooling with the inner wall of the case, so that the binder vapor is prevented from leaking outward from the inner case and condensing by contact with the inner wall of the case.
As such a heat-treating furnace using an inner case, a heat-treating furnace shown in FIG. 7 has been proposed (refer to Patent Document 1).
The heat-treating furnace of FIG. 7 is a heat-treating furnace used for producing a sintered body of ceramic or a metal. For example, when a ceramic material is heat-treated, the heat-treating furnace is aimed at permitting heat treatment without release of impurities such as decomposition gas and combustion gas of a binder to the atmosphere and facilitating maintenance.
As shown in FIG. 7, the heat-treating furnace is configured such that a material 73 to be treated is heat-treated in an inner case 72 which is provided in a furnace body 71 and which is made of a graphite plate and gaseous impurities such as binder vapor produced from the material 73 are discharged from the inner case 72 to outside the furnace body 71. In addition, an impurity collecting trap 75 having an inlet 74 at the top thereof is provided outside the furnace body 71 so that the impurities produced in the inner case 72 are introduced into the impurity collecting trap 75 through an outlet tube 76 and collected.
The heat treating furnace is capable of efficiently removing impurities without discharge to the atmosphere and facilitating maintenance because of its simple configuration, thereby decreasing operating cost and maintenance cost.
However, the heat treating furnace requires not only the inner case disposed in the furnace body but also the outlet tube 76 and the impurity collecting trap 75, and thus the configuration is complicated and causes the problem of increasing the size of equipment and cost.
Although a heat treating furnace including a case with the inner wall covered with a metal muffle is also known, covering the inner wall of the case with the metal muffle has the following problems:
The maximum operating temperature depends on the heat resistance temperature of a metal which constitutes the metal muffle, and thus the operating conditions of the furnace are limited.
A measure against creep deformation of the metal which constitutes the metal muffle is required, and thus the inner dimensions of the furnace are limited.
The inside of the furnace is divided into a heat treatment region partitioned with the metal muffle and another region, and thus the dimensions of the heat treating furnace are increased relative to the necessary effective furnace dimensions, thereby increasing the size of equipment.
The furnace has a double structure, and thus much time is required for assembly and manufacture, thereby increasing the cost.
There is another conceivable heat treating furnace including a case with the inner wall composed of a ceramic board. However, the binder vapor produced in a degreasing step permeates through the ceramic board, reaches the inner wall of the case, and condenses on the inner wall (i.e., the back of a heat insulator) of the case at a temperature lower than the condensation temperature of the binder vapor. The condensed vapor permeates into the heat insulator and solidifies therein to cause the problem of not only increasing the thermal conductivity of the heat insulator but also producing a large difference in thermal conductivity between a portion in which the vapor permeates and a portion in which the vapor does not permeate, causing peeling and breakage of the heat insulator. In particular, when a module heater having a metal heater embedded in a heat insulator is used, there is the problem of decreasing the insulation of the metal heater embedded in the heat insulator within a short time.
Patent Document 1: Japanese Examined Patent Application Publication No. 7-21389